U.S. patent number 4,958,236 [Application Number 07/203,880] was granted by the patent office on 1990-09-18 for image processing method and apparatus therefor.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Hiroyuki Ichikawa, Akihiro Katayama, Nao Nagashima.
United States Patent |
4,958,236 |
Nagashima , et al. |
September 18, 1990 |
**Please see images for:
( Certificate of Correction ) ** |
Image processing method and apparatus therefor
Abstract
In a method of reading an image by dividing it into plural areas
and reading these divided areas in succession, continuity is given
to the data of plural areas by conducting digitization in
overlapping manner over the neighboring areas, in order to avoid
formation of a streak at the boundary of the divided areas.
Inventors: |
Nagashima; Nao (Yokohama,
JP), Ichikawa; Hiroyuki (Tokyo, JP),
Katayama; Akihiro (Kawasaki, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
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Family
ID: |
27566104 |
Appl.
No.: |
07/203,880 |
Filed: |
June 8, 1988 |
Foreign Application Priority Data
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Jun 11, 1987 [JP] |
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62-146311 |
Jun 11, 1987 [JP] |
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62-146312 |
Jun 11, 1987 [JP] |
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62-146313 |
Jun 11, 1987 [JP] |
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62-146314 |
Jun 11, 1987 [JP] |
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62-146315 |
Jun 11, 1987 [JP] |
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62-146316 |
Jun 11, 1987 [JP] |
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62-146317 |
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Current U.S.
Class: |
358/445; 358/296;
358/451; 358/453; 358/480; D18/36 |
Current CPC
Class: |
H04N
1/04 (20130101); H04N 1/0402 (20130101); H04N
1/0417 (20130101); H04N 1/128 (20130101); H04N
1/1911 (20130101); H04N 1/4052 (20130101); H04N
2201/0414 (20130101); H04N 2201/0426 (20130101) |
Current International
Class: |
H04N
1/04 (20060101); H04N 1/191 (20060101); H04N
1/405 (20060101); H04N 001/40 () |
Field of
Search: |
;358/256,280,293,284,445,450,453,451,296 |
References Cited
[Referenced By]
U.S. Patent Documents
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4692812 |
September 1987 |
Hirahara et al. |
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Primary Examiner: Coles, Sr.; Edward L.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data; and
process means for performing a quantization process on the image
data obtained from said reading means to obtain record data to be
used in a recording,
wherein said process means performs, in the recording, a
quantization process of the image data to give continuity to the
plural areas read by said reading means.
2. An apparatus according to claim 1, wherein said process means
performs the quantization process of the image data to obtain
binary data as the record data in an error dispersion method.
3. An image processing apparatus according to claim 2, wherein said
process means comprises memory means for storing error data from an
area preceding an object area, and is adapted, in the quantizing of
the image data of said object area, to conduct the quantizing based
on the error data stored in said memory means, said error data
being generated in the quantizing of the image data.
4. An image processing apparatus according to claim 3, wherein said
process means is further adapted to conduct the quantizing of the
image data of an area succeeding to the object area in an
overlapped manner.
5. An image processing apparatus according to claim 2, wherein said
process means is adapted, in the quantizing of the image data by
the error dispersion method, to conduct the quantizing with a
matrix that does not distribute errors from an object area to a
preceding area.
6. An image processing apparatus according to claim 1, wherein said
process means is adapted, in quantizing the image data of an object
area, to quantize the image data of a preceding area in an
overlapped manner.
7. An image processing apparatus according to claim 6, wherein said
process means is adapted, in quantizing the image data of an object
area, to quantize the image data of preceding and succeeding areas
in the overlapped manner.
8. An image processing apparatus according to claim 1, further
comprising memory means for storing the image data of at least one
of said plural areas, wherein said process means is adapted to
quantize the image data stored in said memory means.
9. An apparatus according to claim 1, further comprising record
means for performing the recording of an image using an ink-jet
method, on the basis of the record data obtained by said process
means.
10. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data;
process means for performing a quantization process on the image
data obtained by said reading means to obtain record data to be
used in a recording; and
memory means for storing information of a jointing portion of the
plural areas,
wherein said process means performs the quantization process to
obtain the record data from the information stored in said memory
means and the image data at the jointing portion.
11. An apparatus according to claim 10, wherein said process means
performs the quantization process of the image data to obtain
binary data as the record data in an error dispersion method.
12. An image processing apparatus according to claim 10, wherein
said memory means is adapted to store information of an area
preceding an object area to be processed by said process means.
13. An image processing apparatus according to claim 12, wherein
the information stored in said memory means is error data generated
in the quantizing of the image data by an error dispersion
method.
14. An image processing apparatus according to claim 13, wherein
said process means is adapted to conduct quantizing based on error
data from an area preceding the object area, stored in the memory
means, and on the image data of said object area.
15. An apparatus according to claim 10, further comprising record
means for performing the recording of an image using an ink-jet
method, on the basis of the record data obtained by said process
means.
16. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data; and
process means for performing a quantization process on the image
data obtained from said reading means to obtain record data to be
used in a recording;
wherein said reading means reads the image data of an area
neighboring an object area to be processed by said process means,
in an overlapping manner, and
wherein said process means performs the quantization process of the
image data read by said reading means in the overlapping manner to
obtain the record data.
17. An image processing apparatus according to claim 16, further
comprising means for extracting the image data of the object area,
from the image data digitized by said process means.
18. An image processing apparatus according to claim 16, wherein
said reading means is adapted to read, in the overlapped manner, a
part of the image data of an area preceding said object area.
19. An image processing apparatus according to claim 16, wherein
said reading means is adapted to read, in the overlapped manner, a
part of the image data of an area succeeding to said object
area.
20. An apparatus according to claim 16, wherein said process means
performs the quantization process on the image data to obtain
binary data as the record data in an error dispersion method.
21. An apparatus according to claim 16, further comprising record
means for performing the recording of an image using an ink-jet
method, on the basis of the record data obtained by said process
means.
22. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data;
process means for performing a quantization process on the image
data obtained from said reading means to obtain record data to be
used in a recording; and
memory means for storing information of a jointing portion of the
plural areas,
wherein said reading means reads the image data of an area
neighboring an object area to be processed by said process means,
in an overlapping manner, and
wherein said process means performs the quantization process on the
information stored in said memory means and the image data read by
said reading means in the overlapping manner, into the record
data.
23. An apparatus according to claim 22, wherein said process means
performs the quantization process on the image data to obtain
binary data as the record data in an error dispersion method.
24. An image processing apparatus according to claim 22, wherein
said memory means is adapted to store information of an area
preceding an object area to be processed by said process means.
25. An image processing apparatus according to claim 24, wherein
the information stored in said memory means is error data generated
in the quantizing of the image data by an error dispersion
method.
26. An image processing apparatus according to claim 22, further
comprising means for extracting the image data of an object area,
from the image data quantized by said process means.
27. An image processing apparatus according to claim 22, wherein
said reading means is adapted to read, in the overlapped manner, a
part of the image data of an area succeeding an object area.
28. An image processing apparatus according to claim 22, wherein
said process means is adapted to conduct the quantizing, in a
jointing portion between an object area and a preceding area, based
on the information stored in said memory means and the image data,
and, in a jointing portion between the object area and a succeeding
area, on the image data obtained in the overlapping reading.
29. An apparatus according to claim 22, further comprising record
means for performing the recording of an image using an ink-jet
method, on the basis of the record data obtained by said process
means.
30. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data; and
process means for digitizing the image data from said reading
means,
wherein said process means is adapted, in digitizing of the image
data, to give continuity to the plural areas read by said reading
means, and
wherein said process means is adapted to digitize the image data
into binary data by an error dispersion method.
31. An apparatus according to claim 30, wherein said process means
is adapted, in digitizing the image data of an object area, to
digitize image data of a preceding area in an overlapping
manner.
32. An apparatus according to claim 31, wherein said process means
is adapted, in digitizing the image data of the object area, to
digitize image data of preceding and succeeding areas in the
overlapping manner.
33. An apparatus according to claim 30, wherein said process means
comprises memory means for storing error data from an area
preceding an object area, and is adapted, in the digitizing of the
image data of the object area, to conduct the digitizing based on
the error data stored in said memory means.
34. An apparatus according to claim 33, wherein said process means
is further adapted to conduct the digitizing of the image data of
an area succeeding the object area in an overlapping manner.
35. An apparatus according to claim 30, wherein said process means
is adapted, in the digitizing of the image data by the error
dispersion method, to conduct the digitizing with a matrix that
does not distribute errors from the object area to a preceding
area.
36. An apparatus according to claim 30, further comprising memory
means for storing the image data of at least one of the plural
areas, and wherein said process means is adapted to digitize the
image data stored in said memory means.
37. An apparatus according to claim 30, further comprising record
means which performs an image recording in an ink-jet manner, on
the basis of the binary data obtained by said process means.
38. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data; and
process means for digitizing the image data from said reading
means,
wherein said process means is adapted, in digitizing of the image
data, to give continuity to the plural areas read by said reading
means; and
wherein said process means is adapted, in digitizing the image data
of an object area, to digitize image data of preceding and
succeeding areas in an overlapping manner.
39. An apparatus according to claim 38, further comprising record
means which performs an image recording in an ink-jet manner, on
the basis of the data digitized by said process means.
40. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data;
process means for digitizing the image data from said reading
means; and
memory means for storing information of a jointing portion of the
plural areas,
wherein said process means is adapted, in the jointing portion of
the plural areas, to conduct the digitizing based on the
information stored in said memory means and on the image data,
and
wherein said process means is adapted to digitize the image data
into binary data by an error dispersion method.
41. An apparatus according to claim 40, wherein said memory means
is adapted to store information of an area preceding an object area
to be processed by said process means.
42. An apparatus according to claim 41, wherein the information
stored in said memory means comprises error data generated in the
digitizing of the image data by the error dispersion method.
43. An apparatus according to claim 42, wherein said process means
is adapted to conduct the digitizing based on the error data from
the area preceding the object area, stored in said memory means,
and on the image data of the object area.
44. An apparatus according to claim 40, further comprising record
means which performs an image recording in an ink-jet manner, on
the basis of the binary data obtained by said process means.
45. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data;
process means for digitizing the image data from said reading
means; and
memory means for storing information of a jointing portion of the
plural areas,
wherein said process means is adapted, in the jointing portion of
the plural areas, to conduct the digitizing based on the
information stored in said memory means and on the image data,
and
wherein said memory means is adapted to store the information of an
area preceding an object area to be processed by said process
means, and the information stored in said memory means is error
data generated by digitizing the image data using an error
dispersion method.
46. An apparatus according to claim 45, wherein said process means
is adapted to conduct the digitizing based on the error data from
an area preceding the object area, stored in said memory means, and
on the image data of the object lens.
47. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data; and
process means for digitizing the image data from said reading
means,
wherein said reading means is adapted to read the image data of an
area neighboring an object area to be processed by said process
means in an overlapping manner, and
wherein said process means is adapted to digitize the image data
read in the overlapping manner, and
wherein said process means is adapted to digitize the image data
into binary data using an error dispersion method.
48. An apparatus according to claim 47, further comprising means
for extracting image data of the object area from the image data
digitized by said process means.
49. An apparatus according to claim 47, wherein said reading means
is adapted to read, in the overlapping manner, a part of the image
data of an area preceding the object area.
50. An apparatus according to claim 47, wherein said reading means
is adapted to read, in the overlapping manner, a part of the image
data of an area succeeding the object area.
51. An apparatus according to claim 47, further comprising record
means which performs an image recording in an ink-jet manner, on
the basis of binary data obtained by said processing means.
52. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data;
process means for digitizing the image data from said reading
means; and
memory means for storing information of a jointing portion of the
plural areas;
wherein said reading means is adapted to read, in an overlapping
manner, the image data of an area neighboring the object area to be
processed by said process means, and
wherein said process means is adapted to conduct digitizing based
on the information stored in said memory means and the image data
in the overlapping manner, and
wherein said process means is adapted to digitize the image data
into binary data by an error dispersion method.
53. An apparatus according to claim 52, wherein said memory means
is adapted to store information of an area preceding the object
area to be processed by said process means.
54. An apparatus according to claim 53, wherein the information
stored in said memory means is error data generated in the
digitizing of the image data by the error dispersion method.
55. An apparatus according to claim 52, further comprising means
for extracting the image data of the object area, from the image
data digitized by said process means.
56. An apparatus according to claim 52, wherein said reading means
is adapted to read, in the overlapping manner, a part of the image
data of an area succeeding the object area.
57. An apparatus according to claim 52, wherein said process means
is adapted to conduct the digitizing, in a jointing portion between
the object area and a preceding area, based on the information
stored in said memory means and the image data, and, in the
jointing portion between the object area and a succeeding area, on
the image data obtained in the overlapping reading.
58. An apparatus according to claim 52, further comprising record
means which performs an image recording in an ink-jet manner, on
the basis of the binary data obtained by said process means.
59. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural area, and for providing image data;
a memory for storing the image data of the plural areas obtained
from said reading means;
means for reading the image data stored in said memory in a
sequence different from a sequence of storage in said memory;
and
process means for digitizing the image data read from said
memory,
wherein said process means is adapted to digitize the image data
into binary data by an error dispersion method.
60. An apparatus according to claim 59, further comprising a second
memory for storing the image data digitized by said process
means.
61. An apparatus according to claim 59, further comprising record
means which performs an image recording in an ink-jet manner, on
the basis of the binary data obtained by said process means.
62. An image processing method comprising:
a reading step of reading an image by dividing the image into
plural areas, and providing image data; and
a process step of digitizing the image data obtained in said
reading step,
wherein said process step is adapted, in the digitizing of the
image data, to give continuity to the plural areas read in said
reading step, and
wherein said process step is adapted to digitize the image data
into binary data by an error dispersion method.
63. A method according to claim 62, wherein said process step is
adapted, in the digitizing of the image data of an object area, to
digitize the image data of a preceding area in an overlapping
manner.
64. A method according to claim 62, wherein said process step is
adapted, in the digitizing of the image data of an object area, to
digitize the image of preceding and succeeding areas in an
overlapping manner.
65. A method according to claim 62, wherein said process step
utilizes memory means for storing error data from an area preceding
the object area, and is adapted, in the digitizing of the image
data of the object area, to conduct the digitizing based on the
error data stored in the memory means.
66. A method according to claim 65, wherein said process step is
further adapted to conduct the digitizing of the image data of an
area succeeding the object area in an overlapping manner.
67. A method according to claim 62, wherein said process step is
adapted, in the digitizing of the image data by the error
dispersion method, to conduct the digitizing with a matrix that
does not distribute errors from an object area to a preceding
area.
68. A method according to claim 62, wherein said process step
further utilizes memory means for storing the image data of at
least one of the plural areas, and is adapted to digitize the image
data stored in the memory means.
69. A method according to claim 62, wherein said process step
utilizes record means which performs an image recording in an
ink-jet manner, on the basis of the binary data obtained by said
process step.
70. An image processing apparatus comprising:
reading means for reading an image by dividing the image into
plural areas, and for providing image data;
process means for performing a quantizing of the image data
obtained from said reading means into record data to be used in an
image recording; and
record means for performing image recording in an ink-jet manner,
based on the record data obtained by said process means,
wherein said process means performs, in a case where the image
recording is performed by said record means, the quantizing of
image data so as to give continuity to the plural areas by said
reading means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image processing method for
processing an image in the form of digital signals and an apparatus
therefor, and more particularly to an image processing method for
pseudo intermediate tone reproduction by digitization of input
image and an apparatus therefor.
2. Related Background Art
There are already known printers using a binary recording method,
forming a record by printing dots or not, such as laser beam
printer (LBP) or ink jet printer. For reproducing an image with
intermediate density such as a photograph or a screentone original
with a copying apparatus employing such a binary printer, the image
data read from such original with intermediate tone are processed
by an image processing circuit for pseudo intermediate tone
reproduction.
The so-called dither method is widely used as one of such pseudo
intermediate tone processing methods.
Said dither method is advantageous in that it is capable of said
pseudo intermediate tone reproduction with a simple hardware
structure and with a low cost, but is associated with following
drawbacks:
(1) a periodic fringe pattern (Moire fringe pattern) is formed on
the reproduced image when the original is a screentone image such
as a printed image, thus deteriorating the image quality; and
(2) when the original contains linetone images or characters, the
image quality is deteriorated as the lines are not satisfactorily
reproduced.
The drawback (1) can be reduced by a smoothing method (spatial
filtering) applied to the read intermediate tone image data, while
the drawback (2) can be reduced for example by edge enhancement,
but it is difficult to obtain satisfactory reproducibility for
various images such as a photograph, an image, a linetone image and
characters. Also such processes require a complicated circuitry,
deteriorating the inherent advantage of the dither method.
Based on these backgrounds, developments are being made on a
so-called error dispersion method as one of such pseudo
intermediate tone processing methods.
The error dispersion method, disclosed for example by R. S. Floyd
and L. Steinberg in "An Adaptive Algorithm for Spatial Grey Scale",
SID 75 Digest, is characterized, in binary digitizing of input
image data, by dispersing the density error between the input image
data and the output image data into surrounding pixels, thereby
conserving the original image density.
Such error dispersion method is superior to the aforementioned
dither method in tone reproduction and resolution, but is
associated with drawbacks of formation of specific stripe patterns
in the uniform density area of the image and of granular noises in
the highlight area of the image due to scattered dot formation.
For avoiding such drawbacks, various methods have been proposed for
example in the U.S. patent applications Ser. Nos. 137,439, 140,029
and 145,593 and a U.S. patent application filed on May 9, 1988,
corresponding to the Japanese Patent Application Nos. 62-121611,
62-121612 and 62-121613.
Such error dispersion method is satisfactorily usable in a copying
apparatus utilizing a raster scanning, but will give rise to a
following drawback when employed in a serial scanning. A copying
apparatus employing such serial scanning is disclosed in the U.S.
patent application Ser. No. 798,672.
In serial scanning, the image is read in succession at first in an
area (a) and then in an area (b), and is subjected to processing by
the error dispersion method. The errors obtained in processing the
image of the area (a) are lost when the processing proceeds to the
area (b). More specifically, in binary digitizing of the area (b),
no carry-over errors from the area (a) are available, so that
appropriate binary digitizing of the area (b) cannot be achieved.
Consequently a discontinuity appears between the processing of the
area (a) and that of the area (b), thus giving rise to a streak or
a black line on the boundary.
Also the binary digitizing of 255th and 256th pixels of each line
in the area (a) requires error information generated in the binary
digitizing of the 1st and 2nd pixels in each line of the area (b).
Proper binary digitizing cannot be achieved due to the lack of such
error information at the boundary of the areas (a) and (b), and a
streak is formed on said boundary.
Now, a further explanation will be provided of the streak formation
on the boundary of the processing areas.
Let us consider a case of utilizing a 3.times.5 error dispersion
matrix shown in FIG. 2A, in which numerals indicate an example of
error distribution ratio.
In FIG. 2B it is assumed that each main scanning line has 256
pixels, and that a notation a(255, 2) indicates the 255th pixel in
the 2nd scanning line, in the sub scanning direction, of the area
(a).
At first let us consider the binary digitizing in an object pixel
a(255, 1). The errors generated in the binary digitizing of said
pixel are added, as will be apparent from the dispersion matrix
shown in FIG. 2A, to pixels b(1, 1), b(1, 2) and b(1, 3).
Also the errors generated in the binary digitizing of a pixel
a(256, 1) are added to pixels b(1, 1), b(1, 2), b(1, 3), b(2, 1),
b(2, 2) and b(2, 3). Similarly the errors generated in the 255th
and 256th pixels in each line of the area (a) are added to the 1st
and 2nd pixels of the lines in the area (b).
Then let us consider the binary digitizing of an object pixel b(1,
1). The errors generated in the binary digitizing of said pixel
b(1, 1) are added, as will be apparent from FIG. 2A, to pixels
a(255, 2), a(256, 2) and a(256, 3).
Also the errors generated in a pixel b(2, 1) are added to pixels
a(256, 2) and a(256, 3). Similarly the erros generated in the 1st
and 2nd pixels in each line of the area (b) are added to the 255th
and 256th pixels of the lines in the area (a).
Therefore, if the error dispersion method is conducted without
consideration of the boundary between the areas (a) and (b) as
shown in FIG. 1A, the errors generated in the binary digitizing of
the 1st and 2nd pixels in each line of the area (b) are not made
available in the binary digitizing of the 255th and 256th pixels in
each line of the area (a), so that said digitizing of the 255th and
256th pixels cannot be achieved in proper manner. Also the errors
generated in the 255th and 256th pixels in each line of the area
(a) have to be added to the 1st and 2nd pixels in the lines of the
area (b). Thus, the binary digitizing of said 1st and 2nd pixels
cannot be achieved in a proper manner unless said errors of the
area (a) are retained until the processing of the area (b). In this
manner a streak is generated at the boundary of the areas (a) and
(b).
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image
processing method free from the above-mentioned drawbacks of the
prior technology and capable of reproducing an image with high
quality and high resolution from any original image, and an
apparatus therefor.
Another object of the present invention is to provide an image
processing method capable of providing a high-quality image by an
improvement over the aforementioned error dispersion method or a
minimum average error method, which is in principle equivalent to
said error dispersion method, and an apparatus therefor.
Still another object of the present invention is to provide an
image processing method capable of high-speed image processing, and
an apparatus therefor.
Still another object of the present invention is to provide an
image processing method capable of reproducing a satisfactory image
with a simple structure, and an apparatus therefor.
Still another object of the present invention is to provide an
image processing method enabling digitization with the error
dispersion method in a copying apparatus utilizing the
serial-scanning method, and an apparatus therefor.
Still another object of the present invention is to provide an
image processing method, in case of dividing the original image
into plural scanning area and effecting digitization in each of
said scanning areas, capable of realizing continuity between
neighboring scanning areas, and an apparatus therefor.
Still another object of the present invention is to provide an
image processing method, in an image processing for intermediate
tone reproduction by dispersing the error generated in said image
processing into surrounding pixels, of conducting the image
processing in an overlapping manner, including an already processed
portion of the image.
Still another object of the present invention is to provide an
image processing method, for intermediate tone reproduction by
dispersing error data generated in the image processing into
surrounding pixels, in which the image processing is conducted in
an overlapping manner including an already processed portion of the
image and a newly processed portion.
Still another object of the present invention is to provide an
image processing method for image reproduction by dispersing the
errors generated in the image processing into surrounding pixels,
featured by storing error data of an image boundary portion and
conducting image processing at such boundary portion based on the
thus stored error data.
Still another object of the present invention is to provide an
image processing method for intermediate tone reproduction by
dispersing error data generated in the image processing into
surrounding pixels, featured by storing error data of an image
boundary portion for use in the succeeding image processing, and
conducting the image processing in an overlapping manner over an
already processed image portion and a newly processed image
portion.
Still another object of the present invention is to provide an
image processing method for effecting, for each of plural areas,
dispersion of error data generated in the image processing into
surrounding pixels, featured by the use of a dispersion matrix
which disperses the errors only in the proceeding direction of
image processing but not in the opposite direction.
Still another object of the present invention is to provide an
image processing method of dividing the original image into plural
scanning areas, storing image signals of each scanning area and
processing said image signals by the error dispersion method.
The foregoing and still other objects of the present invention, and
the advantages thereof, will become fully apparent from the
following description which is to be taken in conjunction with the
attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are schematic views of an example of image
processing showing the drawback to be resolved by the present
invention;
FIGS. 2A and 2B are views showing the draw-back to be resolved by
the present invention;
FIGS. 3A, 3B and 3C are schematic views outlining first and second
embodiments of the present invention;
FIG. 4 is a perspective view of a digital color copying machine
embodying the present invention;
FIG. 5 is a lateral cross-sectional view of the digital color
copying machine shown in FIG. 4;
FIG. 6 is a detailed view around a scanning carriage 34;
FIG. 7 is a view showing mechanisms in a scanner unit 1;
FIG. 8 is a schematic view showing an image reading operation in
the book mode and the sheet mode;
FIG. 9 is a block diagram of the digital color copying machine
embodying the present invention;
FIG. 10 is a timing chart showing an example of image
formation;
FIG. 11 is a block diagram of an image processing unit 107 in first
to fourth embodiments;
FIG. 12 is a block diagram of a block processing circuit 207;
FIG. 13A is a block diagram of a binarizing unit 108 in the first
embodiment;
FIG. 13B is a view of an error dispersion matrix in the first and
second embodiments;
FIG. 14 is a timing chart of the binarizing unit 108 in the first
embodiment;
FIG. 15 is a block diagram of the binarizing unit 108 in the second
embodiment;
FIG. 16 is a timing chart of the binarizing unit 108 in the second
embodiment;
FIGS. 17A, 17B and 17C are schematic views showing the third
embodiment;
FIG. 18A is a block diagram of the binarizing unit 108 in the third
embodiment;
FIG. 18B is a view of the error dispersion matrix in the third and
fourth embodiments;
FIG. 19 is a timing chart of the binarizing unit 108 in the third
embodiment;
FIG. 20 is a schematic view showing the fourth embodiment;
FIG. 21 is a block diagram of the binarizing unit 108 in the fourth
embodiment;
FIG. 22 is a timing chart of the binarizing unit in the fourth
embodiment;
FIG. 23 is a schematic view showing a fifth embodiment;
FIG. 24 is a block diagram of the image processing unit 107 in the
fifth embodiment;
FIG. 25 is a block diagram of the binarizing unit 108 in the fifth
embodiment;
FIG. 26 is a timing chart of the binarizing unit 108 in the fifth
embodiment;
FIG. 27 is a schematic view showing the principle of signal
conversion; and
FIGS. 28, 29 and 30 are views showing examples of signal output
requiring image jointing information.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
At first there will be explained the principle of resolving the
streak formation at the boundary between the scanning areas.
FIG. 3A shows the method of bringing the error generated in the
area (b) shown in FIG. 2B, into the binary digitization of the
pixels in the area (a).
In case of a dispersion matrix which disperses the error in a
direction opposite to the direction of proceeding of image
processing, as shown in FIG. 2A, one for the reasons of streak
black-line formation lies in the fact that the errors generated in
the area (b) in FIG. 2B are not reflected in the binary digitizing
of the area (a). FIG. 3A shows a method of resolving the error by
expanding the area of image reading and binary digitizing to the
area (b), thus involving overlapped reading.
More specifically, based on the fact that the errors from the area
(b) are principally brought from a portion adjacent to the area
(a), the image processing is conducted by overlapped reading
including several pixels (for example 5 pixels) beyond the actual
output area of binary digitizing.
FIG. 3B shows a method of approximation for the carry-over errors
from the area (a) to (b) in a similar principle.
It is therefore possible to suppress the streak at the boundary of
the scanning areas, in the processing of an object area as shown in
FIG. 3C with a dispersion matrix as shown in FIG. 2A by overlapped
reading of several pixels in each line of the object area and of
the neighboring two areas.
The present invention will be clarified in greater detail by
embodiments thereof.
1ST EMBODIMENT
External view
FIG. 4 is an external view of a digital color copying machine
embodying the present invention.
The apparatus can be divided into two portions.
The upper portion shown in FIG. 4 is composed of a color image
scanner unit 1 for generating digital color image data by reading
an original image, and a controller unit 2 which is incorporated in
the scanner unit 1 and is capable processing of the digital color
image data and other functions such as interfacing with external
equipment.
The scanner unit 1 is provided with a mechanism for reading not
only an object or a sheet original placed downwards under an
original cover 11 but also a large-sized sheet original.
An operation unit 10 for entering various information for the
copying machine is connected to the controller unit 2, which gives
instructions to the scanner unit 1 and a printer unit 3 in response
to the entered information.
Also, complex editing can be achieved by replacing the original
cover 11 with a digitizer connected to the controller unit 2.
In the lower part of FIG. 4 there is shown a printer unit 3 for
recording, on a recording sheet, the color digital image signal
released from the controller unit 2. In the present embodiment, the
printer unit 3 is composed of a full-color ink jet printer
utilizing an ink jet recording head disclosed in the Japanese
Unexamined Patent Publication (Kokai) No. 54-59936.
The above-explained two portions are separable and can be placed in
different positions by extending a connecting cable.
Printer unit
FIG. 5 is a lateral cross-sectional view of the digital color
copying apparatus shown in FIG. 4.
The image of an original placed on an original supporting glass 17,
or a projected image, or the image of a sheet original fed by a
sheet feeding mechanism 12, is read by means of an exposure lamp, a
lens 15, and an image device 16, which is a CCD in the present
embodiment, capable of reading a line image in full color. The
image thus read is subjected to various processing in the scanner
unit 1 and the controller unit 2, and is recorded on a recording
sheet in the printer unit 3.
In FIG. 5, the recording sheet is supplied either from a sheet
cassette 20 storing cut sheets of small fixed sizes (A4 - A3 sizes
in the present embodiment) or from a rolled sheet for recordings of
large sizes (A2 - A1 sizes in the present embodiment).
Also manual sheet feeding is possible by inserting a sheet, from an
inlet 22 shown in FIG. 4, along a cover 21 of the sheet feeding
unit.
A pickup roller 24 feeds cut sheets one by one from the cassette
20, and the cut sheet thus fed is transported by transport rollers
25 to a first sheet feeding roller 26.
The rolled sheet 29 is fed by feeding rollers 30, cut into a
predetermined length by a cutter 31 and transported to said first
sheet feeding roller 26.
Also, the manually inserted sheet is transported from the inlet 22
to the first sheet feeding roller 26 by manual inserting rollers
32.
The pickup roller 24, transport rollers 25, rolled sheet feeding
rollers 30, first sheet feeding rollers 26 and manual inserting
rollers 32 are driven by an unrepresented sheet feeding motor
(composed of a DC servo motor in the present embodiment) and
respectively on-off controlled by solenoid clutches attached to
these rollers.
When a printing operation is started by an instruction from the
controller unit 2, the recording sheet supplied from either of the
above-explained paths is transported to the first sheet feeding
rollers 26. After a predetermined loop is formed in the sheet for
avoiding skewed advancement, said feeding rollers 26 are rotated to
transfer the sheet to second sheet feeding rollers 27.
Between the first sheet feeding rollers 26 and the second sheet
feeding rollers 27, the recording sheet is given a buffer loop of a
predetermined amount for achieving exact sheet advancement between
the second sheet feeding roller 27 and transport rollers. A buffer
sensor 33 is provided for detecting the amount of said buffer loop.
Constant formation of said buffer loop during the sheet
transportation reduces the load on the second sheet feeding rollers
27 and the transport rollers 28, particularly in the transportation
of large-sizes sheet, and enables exact sheet advancement.
In the printing operation with the recording head 37, a carriage 34
supporting said recording head 37 performs a reciprocating motion
on a carriage rail 36 by means of a scanning motor 35. During the
forward motion the image is printed on the recording sheet, and, in
the reverse motion, the sheet is advanced by a predetermined amount
by a sheet feeding motor 28. In this operation, the sheet feeding
motor is so controlled as to maintain the predetermiend amount of
buffer loop, in cooperation with the buffer sensor 33.
The printed recording sheet is discharged onto a discharge tray 23,
and the printing operation is completed.
Now, reference is made to FIG. 6 for explaining the details of the
structure around the carriage 34.
A sheet feeding motor 40, for intermittent advancement of the
recording sheet, drives the second sheet feeding rollers 27 through
a clutch 43, and the transport rollers 28.
A scanning motor 35 moves the carriage 34 in a direction A or B by
means of a scanning belt 42. In the present embodiment, for
achieving exact control for sheet feeding, stepping motors are
employed for the sheet feeding motor 40 and the scanning motor
35.
When the recording sheet reaches the second sheet feeding rollers
27, the clutch 43 therefor and the sheet feeding motor 40 are
activated to transport the recording sheet on a platen 39, to the
transport rollers 28.
The sheet is detected by a sheet sensor 44 positioned on the
platen, and the information from said sensor is utilized for
position control and jamming detection.
When the recording sheet reaches the transport rollers 28, the
clutch 43 and the sheet feeding motor 40 are turned off, and the
sheet is brought into close contact with the platen 39 by suction
from the interior of the platen 39 caused by an unrepresented
suction motor.
Prior to the image recording operation on the recording sheet, the
carriage 34 is moved to the position of a home position sensor 41
Then, in the course of forward motion in the direction A, inks of
cyan (C), magenta (M), yellow (Y) and black (K) are emitted from
the recording head 37 at predetermined positions to achieve image
recording. After the image recording of a predetermined length, the
carriage 34 is stopped and is reversed in the direction B to the
position of the home position sensor 41. During said reverse
motion, the sheet feeding motor 40 drives the transport rollers 28
to advance the recording sheet in a direction C by an amount
corresponding to the amount of recording by the recording head
37.
In the present embodiment, the recording head 37 is an ink jet
recording head containing 4 assemblies of 256 nozzles each.
When the carriage 34 is returned to the position detected by the
home position sensor 41, there is conducted a recovery operation
for the recording head 37. This operation is for achieving a stable
recording operation, and consists of a pressure application to the
recording head 37 and/or a dummy ink emission according to
predetermined conditions of sheet feeding time, temerature and
emission time, in order to prevent defective ink emission at the
start of ink emission caused for example by viscosity change of the
ink remaining in the nozzles of the recording head 37.
Image recording on the entire surface of the recording sheet can be
achieved by repeating the above-explained procedure.
Scanner unit
Now reference is made to FIGS. 7 and 8 for explaining the function
of the scanner unit 1.
FIG. 7 shows the structure in the scanner unit 1.
A CCD unit 18, consisting of a CCD 16, a lens 15 etc. moves along a
rail 54 by means of a main scanning driving system consisting of a
main scanning motor 50 fixed on the rail 54, pulleys 51, 52 and a
wire 53, thereby reading the image on the original supporting glass
17 in the main scanning direction. A light shielding plate 55 and
home position sensor (HP sensor) 56 are used for position control
in moving the CCD unit 18 to a main scanning home position provided
in a correction area 68.
The rail 54 is supported by rails 65, 69 and is moved by a sub
scanning driving system consisting of a sub scanning motor 60,
pulleys 67, 68, 71, 76, shafts 72, 73 and wires 66, 70. A light
shielding plate 57 and home position sensors 58, 59 are used for
position control in moving the rail 54 to sub scanning home
positions for a book mode for reading a book or an article placed
on the glass 17 or a sheet mode for reading a sheet original.
A sheet feeding motor 61, sheet feeding rollers 74, 75, pulleys 62,
64 and a wire 63 constitute a mechanism for feeding sheet
originals. Said mechanism is positioned above the original
supporting glass 17, and sheet originals placed downwards are
advanced by a predetermined amount with the sheet feeding rollers
74, 75.
FIG. 8 illustrates the image reading operation in the book mode and
the sheet mode.
In the book mode the CCD unit 18 is moved to the book mode home
position (black mode HP) provided in the correction area 68, and
the entire surface of the original placed on the glass 17 is read
with the CCD unit 18, starting from said home position.
Prior to the scanning of the original, shading correction, black
level correction, color correction etc. are conducted in the
correction area 68. Thereafter the scanning motion in the main
scanning direction is started by the main scanning motor 50. After
the image reading of an area (1), the main scanning motor 50 is
reversed and the sub scanning motor 60 is activated, thereby moving
the CCD unit in the sub scanning direction to the correction area
for an area (2). Then, after shading correction, black level
correction, color correction etc. if required, the area (2) is read
is the same manner as in the area (1).
Areas (1)-(7) are read by repeating the above-explained scanning
operation, and, after the image reading of the area (7), the CCD
unit 18 is returned to the book mode home position.
In the present embodiment, for reading an original of A2 size at
maximum, there is in fact required a larger number of scanning
operations, but the scanning operations are simplified in this
explanation for ease of understanding.
In the sheet mode, the CCD unit 18 is moved to a sheet mode home
position, and the entire surface of the sheet original is read by
repeatedly reading the area (8) and intermittently activating the
sheet feeding motor 61.
Prior to the scanning motion, shading correction, black level
correction, color correction etc. are conducted in the correction
area 68, and then the scanning motion is started in the main
scanning direction by the main scanning motor. After the completion
of the forward reading motion in the area (8), the main scanning
motor 50 is reversed, and the sheet feeding motor 61 is
simultaneously activated to move the sheet original by a
predetermined amount in the sub scanning direction. The
above-explained operation is repeated to read the entire surface of
the sheet original.
When the above-explained image reading operation is designed for
same-size image reproduction, the CCD unit 18 can in fact read a
wide area as shown in FIG. 5. This is because the digital color
copying apparatus of the present embodiment has functions of image
enlargement and image reduction. Since the recording head 37 can
record 256 bits only at a time as explained before, an image
reduction by 50% for example requires image information of a
doubled area of 512 bits at least.
Also the scanner unit 1 is capable of overlapped image reading over
plural scanning areas.
In the present embodiment, each scanning area shown in FIG. 8 has
256 pixels in the sub scanning direction.
The overlapped reading means simultaneously reading 5 pixels each
of two neighboring areas. Therefore, in the overlapped reading, 266
pixels are read including two neighboring areas.
Explanation of block diagram
In the following there will be explained functional blocks of the
digital color copying apparatus of the present embodiment shown in
FIG. 9.
Control units 102, 111, 121 respectively control the scanner unit
1, controller unit 2 and printer unit 3, and are each composed of a
microcomputer, a program ROM, a data memory, a communication
circuit etc. The control units 102-111 and the control units
111-121 are connected by communication lines, and so-called
master-slave control is adapted in which the control units 102, 121
are operated by the instructions of the control unit 111.
In the function of a color copying apparatus, the control unit 111
performs control operations in response to the input from the
operation unit 10 and the digitizer 114.
The operation unit 10 is composed for example of a liquid crystal
display provided thereon with a touch panel composed of transparent
electrodes to enable selections such as selections of colors and
editing operations. It is also provided with separate keys of
higher frequency of use, such as a start key for starting a copying
operation, a stop key for interrupting the copying operation, and a
reset key for resetting the operation mode to a standard state.
The digitizer 114, for entering positional information indicating
the area of trimming, masking, color conversion etc., is connected
as an option when a complex editing is required.
The control unit 111 also controls an I/F control unit 112, which
is a control circuit for a general parallel interface such as
IEEE-488 or so-called GP-IB interface, and said interface is
utilized for the input/output of image data with external equipment
or remote control by external equipment.
In addition, the control unit 111 controls a multi-level value
synthesis unit 106, an image processing unit 107, a binary
digitizing unit 108, a binary synthesis unit 109 and a buffer
memory 110 for effecting various image processings.
The control unit 102 controls a mechanical drive unit 105 for
controlling the mechanism of the above-explained scanner unit 1, an
exposure control unit 103 for lamp exposure control in reading a
reflective original, and an exposure control unit 104 for exposure
control of a halogen lamp 90 when a projector is used. The control
unit 102 also controls an analog signal processing unit 100 and an
input image processing unit 101 for effecting various image
processings.
The control unit 121 controls a mechanical drive unit 105 for
controlling the mechanism of the above-explained printer unit 3,
and a synchronization delay memory 115 for absorbing the
fluctuation in time of the mechanical function of the printer unit
3 and for compensating the delay resulting from mechanical
arrangement of the recording heads 117-120.
In the following, the flow of image processing will be explained in
more detail, with reference to FIG. 9.
The image focused on the CCD 16 is converted into an analog
electrical signal, which is supplied to the analog signal
processing unit 100 in serial manner, for example in cycles of red,
green and blue.
The analog signal processing unit 100 performs the sampling and
holding, dark level correction and dynamic range control for each
of red, green and blue colors, and performs an analog-to-digital
(A/D) conversion to obtain serial multi-value digital image signals
(8 bits for each color in the present embodiment), which are sent
to the input image processing unit 101.
Said unit 101 conducts the shading correction, color correction and
gamma correction which are required in the image reading system, in
the form of a serial multi-value digital image signal.
The multi-value synthesis unit 106 of the controller unit 2
performs selection and synthesis of the serial multi-value digital
image signal supplied from the scanner unit 1 and the serial
multi-value digital image signal supplied from the parallel
interface. The image data, thus selected and synthesized, are sent
to the image processing unit 107 in the form of the serial
multi-value digital image signal.
The image processing unit 107 conducts edge enhancement, black
extraction, undercolor removal (UCR) and masking for color
correction for the recording inks to be used in the recording heads
117-120. The obtained output signal, in the form of a serial
multi-value digital signal, is supplied to the binary digitizing
unit 108 and the buffer memory 110.
The binary digitizing unit 108 binary digitizes the serial
multi-value digital image signal by the error dispersion method to
obtain binary parallel image signals of four colors. The image data
of four colors are sent to the binary synthesis unit 109, while the
image data of three colors are sent to the buffer memory 110.
The binary synthesis unit 109 performs selection and synthesis of
the binary parallel image signals of three colors supplied from the
buffer memory 110 and those of four colors from the binary
digitizing unit 108 to obtain binary parallel image signals of four
colors.
The buffer memory 110 performs the input and output of multi-value
image data or binary image data through the parallel interface.
The synchronization delay memory 115 of the printer unit 3 absorbs
the fluctuation in time of the mechanical function of the printer
unit 3 and compensates the delay resulting from the mechanical
arrangement of the recording heads 117-120, and internally
generates timing signals required for driving the recording heads
117-120.
A head driver 116, which is an analog driving circuit for driving
the recording heads 117-120, internally generates signals for
directly driving said heads.
The recording heads 117-120 respectively emit inks of cyan (C),
magenta (M), yellow (Y) and black (K), thus recording an image on a
recording sheet.
Timing signals
FIG. 10 is a timing chart showing signals in the circuit blocks
explained in FIG. 9.
A signal BVE indicates the effective image section in each scanning
operation of the main scanning explained in relation to FIG. 8. The
image output of the entire area is obtained by repeating the signal
BVE.
A signal VE indicates the effective image section in each line read
by the CCD 16. The signal VE is effective only when the signal BVE
is effective.
A signal VCK is a clock signal for the image (video) data VD. The
signals BVE and VE change in synchronization with the signal
VCK.
A signal HS is used for repeating effective and ineffective
sections in discontinuous manner in a line of the signal VE, and is
not used if the signal VE is continuously effective during a line.
It also indicates the start of image output of a line.
Circuit structure of image processing unit 107
Now reference is made to FIG. 11 for explaining the circuit
structure of the image processing unit 107.
The color-sequential multi-value image information of three colors
(cyan, magenta and yellow) supplied from the multi-value synthesis
unit 106 shown in FIG. 9 is supplied to a color conversion circuit
201, for electrically converting a particular color, designated for
example by the digitizer 114, into another color. Said circuit
enables conversion of a particular color in the original (for
example the color of fabric in a designing of clothing) into an
arbitrary color.
A serial-parallel (S/P) signal conversion circuit 203 separates the
color-sequential multi-value image information of three colors into
respective colors for the color processing in a following masking
circuit 204.
The masking circuit 204 corrects the input color information, in
consideration of the color reproducing performance of the printer,
according to the following equation: ##EQU1## wherein
Y, M, C: input data
Y', M', C': output data
a.sub.11 -a.sub.33 : correction coefficients
A black extraction circuit 202 extracts the black (K) component
from the color-sequential multi-value image information of three
colors. A color component of lowest density among the components of
cyan (C), magenta (M) and yellow (Y) is extracted as the black
component.
An undercolor removal (UCR) circuit 205 performs calculation on the
black (K) component extracted in the black extraction circuit 202
and the three components of cyan (C), magenta (M) and yellow (Y)
for improving the color reproducibility. The color-sequential
multi-value color information of three colors (cyan, magenta and
yellow) is converted by this circuit into the color-sequential
multi-value color information of four colors (cyan, magenta, yellow
and black).
Said undercolor removal circuit 205 may also be utilized for gamma
correction and image data offsetting, if necessary.
An edge enhancement circuit 206 extracts the edge component for
each color and adds or subtracts said edge component to or from the
original image data, thereby improving the reproduction of fine
lines and giving emphasis to the image. The edge extraction is
conducted for example by a 3.times.3 matrix processing as shown
below: ##STR1##
A block processing circuit 207 reduces particular stripe patterns
generated by the error dispersion method in the image, particularly
in the highlight portion thereof.
The image data processed in the block processing circuit 207 are
binary digitized in the binary digitizing unit 108 utilizing the
error dispersion method.
Said block processing circuit 207 is designed to eliminate stripe
patterns which are generated in the vicinity of a steep density
change in a highlight image area. This procedure is achieved by
dividing the image into 4.times.4 matrixes for example, and
detecting whether the block is in a highlight image portion. If the
object block is in the highlight area, the density of the pixels in
the block is concentrated to a particularly pixel to form a pseudo
screen dot, thereby preventing the cluster formation of dots and
thus avoiding the formation of particular stripe patterns.
Now reference is made to FIG. 12 for explaining the circuit
structure of said block processing circuit 207.
A maximum detection circuit 210 and a minimum detection circuit 211
respectively detect a maximum density D.sub.max and a minimum
density D.sub.min in the pixlels of the 4.times.4 matrix divided as
a block.
A sum calculation circuit 212 determines the total sum D.sub.sum of
the density of the pixels in said block.
A judgement circuit 213 performs discriminations, based on the
maximum density D.sub.max, minimum density D.sub.min and sum
D.sub.sum, according to the following conditions:
When these two conditions are satisfied, a dot forming circuit 215
forms a pseudo screen dot for the pixels in the block. If the
conditions are not satisfied, the image data are merely
transmitted.
A delay circuit 214 is a line buffer for delaying the pixels during
the above-mentioned judgement, and should have a capacity of 4
lines in case of forming a 4.times.4 matrix as each block.
The dot forming circuit 215 performs the following process on the
pixels in the block. The following example shows a case of a
4.times.4 matrix: ##STR2## wherein:
# pixel where density is decreased
* pixel where density is concentrated
The density is decreased to 1/n in each pixel #, and the density is
correspondingly increased in the pixel *, so as to conserve the
total density in the block. The advantage of the error dispersion
method is not lost by this process, since the total density is
conserved.
This process may be conducted in a finer manner by increasing the
judging conditions mentioned above in combination with the density
distribution and the processing blocks.
It is also possible to employ different blocks, such as the blocks
A and B shown above, for different colors, in order to prevent
overlapping of the dots of different colors.
The probability of dot formation is high at the pixel where the
density is concentrated. It is therefore possible to change the
position of density concentration by changing the block as
indicated by A and B, thereby reducing the probability of
concentration of the dots of different colors.
Such block processing allows to the dispersion of printed dots and
the prevention of the formation of stripe patterns in the vicinity
of a steep density change in the highlight portion.
In the following there will be explained the circuit structure of
the binary digitizing circuit 108 using FIGS. 13A and 13B.
It is assumed that the image data are arranged two-dimensionally,
and the image data at the i-th pixel in the main scanning direction
and j-th pixel in the sub scanning direction are indicated by
D.sub.ij.
FIG. 13B shows an error distribution matrix showing the mode of
division and distribution, to the surrounding pixels, of the error
data generated in the binary digitizing of image data D.sub.ij of
an object pixel entered in the binary digitizing unit 108. The
suffix (ij) indicates that the error is generated from the image
data D.sub.ij.
In the binary digitizing of the present embodiment, the errors are
accumulated by the successive shift of the matrix, shown in FIG.
13B in the main scanning direction, and the binary digitizing is
conducted on the sum of the errors distributed from plural pixels
and the image data entered for the object pixel.
The matrix shown in FIG. 13B is equivalent to that shown in FIG.
2A.
FIG. 13A shows the circuit structure of the binary digitizing unit
of the present embodiment.
In FIG. 13A, each of delay units 301-310 is composed of four
flip-flops, and delays the color-sequential image data by 4 clock
signals or a pixel, for processing of the image data of each
color.
There are provided adders 311-322. The adders 311-321 are used for
additions or subtraction of error data for calculating the error in
the error dispersion matrix, while the adder 322 is used for adding
the error data calculated in said matrix with the input image
data.
Each of error line memories 323, 324, composed for example of FIFO
(first-in-first-out) memories, stores the calculated errors of each
line and effects a delay of a line.
There are also provided an error distribution unit 325 composed of
a read-only memory (ROM), a comparator 326 for comparing the result
of the addition of the error data and the image data with a
predetermined threshold value, and an AND gate 327 for controlling
the data output by a control signal A.
In the following there will be explained the function of the
circuit shown in FIG. 13A.
The image data supplied to the binary digitizing unit 108 are
added, in the adder 322, with the error data supplied from the
delay unit 310, and are supplied to the error distribution unit
325, which releases error data (a, b, c, d) of a predetermined
ratio utilizing a look-up table stored in a ROM. The comparator 326
compares the output of the adder 322 with a predetermined threshold
value and releases a binary output "1" or "0". The output signals
of the comparator 326 are transmitted only in the necessary pixels
by the gate 327.
In response to the image data D.sub.ij, the error distribution unit
325 releases error data a.sub.ij, b.sub.ij, c.sub.ij and d.sub.ij.
The error data d.sub.ij are delayed corresponding to four colors in
the delay unit 301, and, when the processing proceeds in the main
scanning direction, are added in the adder 311 with the error data
c.sub.i+1,j of the same color generated from the image data
D.sub.i+1,j.
The addition of error data is repeated thereafter in the adders
302, 312, 303, 313, 304 and 314 with the progress of the
processing, and the output of the adder 314 is supplied to the line
memory 323. The added error data thus stored in the line memory 323
are read therefrom after the delay of a line, and supplied to the
adder 315.
Thereafter the error data generated in other pixels are added in
the adders 305, 316, 306, 317, 307, 318, 308 and 319. After the
addition, in the adder 319, of the error data c.sub.i+4,j+1
generated from the input image data D.sub.i+4,j+1, the result is
supplied to the line memory 324. The error data released from the
line memory 324 are subjected to the addition of error data in the
adders 320, 321, and are added with the image data in the adder
322. Subsequently the sum of the error data and the image data is
supplied to the error distribution unit 325 and the comparator 326.
The binarizing process is thereafter continued in the same
manner.
The above-explained procedure can be summarized, for example for
the input image data D.sub.ij, in the following manner: ##EQU2##
wherein:
DD: data after processing
D: image data
i: pixel number in a line (for each color)
j: line number
Now reference is made to a timing chart shown in FIG. 14 for
explaining the function of the circuit.
The timing chart shown in FIG. 14 shows a case of a single color
for facilitating the understanding of the function. In the actual
circuit, the number of pixels is multiplied by the number of
colors, namely four times for four colors.
When the overlapped reading is conducted over n pixels in the
neighboring areas (5 pixels in each area in case of FIG. 3C), the
binary digitizing is conducted in succession from the first pixel
entered to the comparator 326. The binarized output data from the
comparator 326 are released by the output control unit 327 only by
a required number of pixels, starting from the (n+1)-th pixel
(first pixel of the object area in case of FIG. 3C). Thus the image
data of 2n+256 pixels are entered, as shown in FIG. 14, in
synchronization with VE1, because of the overlapped reading of 256
pixels in the object area and n pixels in each of the neighboring
areas. These data are binary digitized, and the thus processed data
are transmitted by the gate 327 according to the control signal A
to obtain the data of 256 pixels of the required object area.
As explained in the foregoing, the discontinuity in the image at
the jointing portion can be reduced by an overlapped reading of the
image including the areas neighboring the object area and by
obtaining the output from the areas in which the errors from said
neighboring areas are accumulated.
In the present embodiment, the error distribution unit 325 relies
on table conversion by a ROM, but it is naturally possible to use a
RAM or a multiplier.
As explained in the foregoing, it is not necessary to add hardware
even when there is employed an error dispersion matrix for
dispersing errors into the areas neighboring the object area, and
the streak at the jointing portion of the image can be reduced to a
practically acceptable level, by simple overlapped reading of the
neighboring areas and binary digitizing.
Second Embodiment
In the foregoing embodiment, it is possible to reduce the streak at
the boundary of the areas in the binary digitizing of the object
area, by an overlapped reading of several pixels in each line of
two neighboring areas, and binary digitizing of the pixels thus
obtained by overlapped reading.
In the second embodiment to be explained in the following, there is
employed a line buffer for retaining the carry-over errors from a
preceding area, and, in reading the object area, several pixels in
each line of a succeeding area are simultaneously read. In
processing the 1st and 2nd pixels of each line in the object area,
the data of the carry-over errors are read from said line buffer to
achieve exact binary digitizing of the object area.
In the second embodiment, the structures shown in FIGS. 4 to 12 are
the same as those of the first embodiment and will not, therefore,
be explained.
Referring to FIG. 8, the second embodiment effects binary
digitizing by an overlapped reading only covering the succeeding
area neighboring the object area.
FIG. 15 is a circuit diagram of the binary digitizing unit 108
shown in FIG. 9, partially modified from the circuit of the first
embodiment shown in FIG. 13A.
The circuit shown in FIG. 15 is different in the presence of a
joint error memory 328, from that shown in FIG. 13A.
In FIG. 15, the same components as those in FIG. 13A are
represented by the same numbers and will not be explained
further.
The joint error memory 328 is used for storing the error data in
the joint portion between the object area and the succeeding area
shown in FIG. 3C.
A control signal C is used for controlling the data output from the
AND gate 327.
In the following there will be explained the function of the image
jointing unit, with reference to FIGS. 15 and 16.
FIG. 16 is a timing chart showing the function for a single color
for facilitating understanding.
A scanning operation of the CCD unit 18 in the scanner unit 1
explained before provides image data of plural lines.
In the first scanning operation a switch SW1 is closed with the
timing of a control signal B shown in FIG. 16 whereby the error
data to be added to the image data of the 257th and 258th pixels in
each line of the area (a) shown in FIG. 3A (corresponding to the
1st and 2nd pixels in the area (b)) are supplied from the delay
unit 310 and stored in the joint error memory 328. These error data
are read from the joint error memory 328, in synchronization with
the image data of the 1st and 2nd pixels of corresponding lines
obtained in the succeeding scanning operation. For this purpose a
switch SW2 is closed with the timing of a control signal A shown in
FIG. 16. The error data thus read are sent through the switch SW2
to the adder 322, then added to the corresponding image data, and
supplied to the error distribution unit 325 and the comparator 326
for error distribution and binary digitizing. Then, the error data
to be added to the image data of the 257th and 258th pixels of the
area (b) (corresponding to the 1st and 2nd pixels of an area
succeeding the area (b)) are stored in the joint error memory 328
through the switch SW1 as in the first scanning operation.
Thereafter the writing and reading of the error data of the
jointing portion to and from the joint error memory 328 are
conducted according to the timing shown in FIG. 16.
As explained in the foregoing, a smooth output image without
streaking in the jointing portion can be obtained by considering
the errors affecting the jointing portion through an overlapped
reading of the succeeding area, and by conserving the error
information of the jointing portion.
In this manner it is possible to eliminate the streaking at the
jointing portion of the image areas by an overlapped reading of the
object area and the succeeding area and by the use of a memory for
storing the errors carried over from the preceding image area.
Third embodiment
The foregoing first and second embodiments are to eliminate the
streak formation at the jointing portion of the image through the
use of a dispersion matrix shown in FIG. 2A.
In the processing with the dispersion matrix shown in FIG. 2A, the
binary digitizing of the 255th and 256th pixels in each line of the
area (a) cannot be exactly achieved without the error information
generated in the 1st and 2nd pixels in each line of the area (b)
shown in FIG. 2B. Consequently, for achieving correct binary
digitizing of the 255th and 256th pixels in each line of the area
(a), the form of the dispersion matrix may be so modified that the
errors generated in the area (b) are not added to the area (a).
A dispersion matrix shown in FIG. 17A is so constructed that the
errors are not distributed to the pixels in a direction opposite to
tha main scanning direction. Said dispersion matrix is formed as a
4.times.4 matrix, but it may assume any form as long as the errors
are not distributed in the pixels positioned in a direction
opposite to the main scanning direction.
When the dispersion matrix shown in FIG. 17A, which does not
distribute the errors to the pixels in a direction opposite to the
main scanning direction, is employed, the binary digitizing of the
255th and 256th pixels in each line of the area (a) shown in FIG.
2B can be achieved correctly since no errors are to be added to the
255th and 256th pixels in each line of the area (a) from the 1st
and 2nd pixels in each line of the area (b). However the binary
digitizing of the 1st and 2nd pixels in each line of the area (b)
cannot be achieved correctly since there are no carryover errors
from the area (a) as explained before.
In order to resolve this drawback, it is possible to effect an
overlapped reading, covering several pixels (for example 5 pixels)
adjacent to the area (b) in each line of the area (a) in reading
the area (b) as shown in FIG. 17B and to obtain the result of
processing only from the image area (b).
This method does not exactly reproduce the carry-over errors from
the area (a), but the approximate data produced in this method is
practically acceptable since only the pixels of the area (a) close
to the area (b) affect the area (b).
It is therefore possible to eliminate the streak formed at the
boundary between the image areas by using a dispersion matrix as
shown in FIG. 17A and reading several pixels (for example 5 pixels)
in each line of the preceding area simultaneously with the reading
of the object area as shown in FIG. 17C.
The structures of the first embodiment shown in FIGS. 4 to 12 are
also employed in the third embodiment, and will not, therefore, be
explained again.
Referring to FIG. 8, the image reading in the third embodiment is
conducted in overlapping manner, covering only the preceding area
adjacent to the object area for binary digitizing.
FIGS. 18A and 18B show the circuit structure of the binary
digitizing unit 108 employed in the third embodiment.
The image data are arranged two-dimensionally, and D.sub.ij
indicates the image data of a pixel at an i-th position in the main
scanning direction and a j-th position in the sub scanning
direction.
FIG. 18B shows an error distribution matrix which defines the
distribution, to 15 surrounding pixels, with predetermined
proportions, of the error generated in the binary digitizing of the
image data D.sub.ij of an arbitrary pixel entered to the binary
digitizing unit 108. The suffixes i, j attached to the error data
indicate that said error is generated from the image data
D.sub.ij.
In this manner, in the present binary digitizing, the errors are
accumulated by the successive shifting of the matrix, shown in FIG.
18B in the main scanning direction by a pixel at a time, and the
binary digitizing process is conducted on the sum of the image data
of the object pixel and the sum of errors distributed from plural
pixels.
FIG. 18A is a circuit diagram showing the binary digitizing unit
employed in the present embodiment.
In FIG. 18A, each of delay units 401-412 is composed of four
flip-flops, and delays the color-sequential image data by 4 clock
signals or a pixel, for processing of the image data of each
color.
There are provided adders 413-427. The adders 413-426 are used for
additions or subtractions of error data for calculating the errors
in the error dispersion matrix, while the adder 427 is used for
adding the error data calculated in said matrix with the input
image data.
Each of error line memories 428, 430, composed for example of FIFO
(first-in-first-out) memories, stores the calculated errors of each
line and effects a delay of a line.
There are also provided an error distribution unit 431 composed of
a read-only memory (ROM), a comparator 432 for comparing the result
of addition of the error data and the image data with a
predetermined threshold value, and a gate 433 for controlling the
output of the data.
In the following there will be explained the function of the
circuit shown in FIG. 18A.
The image data supplied to the binary digitizing unit 108 are
added, in the adder 427, with the error data supplied from the
delay unit 412, and are supplied to the error distribution unit
431, which releases error data (a, b, c, d, e, f, g) of a
predetermined ratio utilizing a look-up table stored in a ROM. The
comparator 432 compares the output of the adder 427 with a
predetermined threshold value and releases a binary output "1" or
"0". The output signals of the comparator 432 are transmitted only
in the necessary pixels by the gate 433.
In response to the image data D.sub.ij, the error distribution unit
431 releases error data a.sub.ij, b.sub.ij, c.sub.ij, d.sub.ij,
e.sub.ij, f.sub.ij and g.sub.ij. The data g.sub.ij are delayed
corresponding to four colors in the delay unit 401, and, when the
processing proceeds in the main scanning direction, are added in
the adder 413 with the error data g.sub.i+1,j of the same color
generated from the image data D.sub.i+1,j.
Thereafter the addition of error data is repeated in the adders
402, 414, 403 and 415 with the progress of the processing, and the
output of the adder 415 is supplied to the line memory 428. The
added error data thus stored in the line memory 428 are read
therefrom after the delay of a line, and supplied to the adder
416.
Thereafter the error data generated in other pixels are added in
the adders 404, 417, 405, 418, 406 and 419. After the addition, in
the adder 419, of the error data c.sub.i+3,j+1 generated from the
input image data D.sub.i+3,j+1, the result is supplied to the line
memory 427. The error data released from the line memory 427 are
supplied to the adder 420, then processed in the similar manner in
the adders 407, 421, 408, 422, 409 and 423, and, after the addition
of the error data in the adder 423, supplied to the line memory
430.
The error data released from the line memory 430 are subjected to
the additions of error data in the adders 424, 410, 425, 411, and
426, and further added with the image data in the adder 247. The
result of addition of the error data and the image data are
supplied to the error distribution unit 331 and the comparator
332.
The above-explained procedure can be summarized, for example for
the input image data D.sub.ij, in the following manner: ##EQU3##
wherein:
DD: data after processing
D: image data
i: pixel number in a line (for each color)
j: line number
Now reference is made to a timing chart shown in FIG. 19 for
explaining the function of the circuit. Said timing chart shows a
case of a single color for facilitating the understanding of the
function. In the actual circuit, the number of pixels is multiplied
by the number of colors, namely four times for four colors.
When the overlapped reading is conducted over n pixels in the
neighboring area (5 pixel in FIG. 17C for example), the binary
digitizing is conducted in succession from the first pixel entered
to the comparator 432. The binarized output data from the
comparator 432 are released by the output control unit 433 only by
a required number of pixels, starting from the (n+1)-th pixel
(corresponding to the 1st pixel in the object area in FIG. 17C).
Thus, the image data of n+256 pixels are entered, as shown in FIG.
14, in synchronization with the signal VE1, because of the
overlapped reading of 256 pixels in the object area and n pixels in
the preceding area. These data are binary digitized, and the thus
processed data are transmitted according to the control signal A to
obtain the data of 256 pixels.
As explained in the foregoing, the streak formation at the jointing
portion of the image areas can be prevented by employing a matrix
which does not distribute the errors in an area preceding the
object area, and effecting binary digitizing by an overlapped
reading covering the preceding area.
In the present embodiment, the error distribution unit 431 relies
on a table conversion utilizing a ROM, but there may naturally be
employed a RAM or a multiplier.
Fourth embodiment
The foregoing third embodiment employs a matrix (FIG. 17A) which
does not distribute the errors in the pixels in a direction
opposite to the main scanning direction with respect to the object
pixel, thereby avoiding the distribution of the errors, generated
in the 1st and 2nd pixels in each line of the succeeding area, to
the object area and thus achieving correct binary digitizing of the
255th and 256th pixels in each line of the object area. Also in the
binary digitizing of the 1st and 2nd pixels in each line of the
succeeding area, there should only be considered the errors carried
over from the object area to the succeeding area, so that the
binary digitizing is conducted by an overlapped reading, covering
the object area.
In the fourth embodiment explained in the following, there is
employed a line buffer for conserving the carry-over errors from
the 255th and 256th pixels in each line of the preceding area,
shown in FIG. 20, for addition to the 1st and 2nd pixels in each
line of the object area. Thus, in the processing of the object
area, the carry-over error data are read from said line buffer and
added to the 1st and 2nd pixels in each line of the object
area.
Thus, it is possible to completely eliminate the streak generated
at the boundary of the image areas by employing a dispersion matrix
as shown in FIG. 17A and also employing a line buffer for
conserving the carry-over errors from the pixels of the preceding
area, for addition to the pixels in the object area.
In the fourth embodiment, the structures shown in FIGS. 4 to 12 are
the same as those employed in the first embodiment and will not,
therefore, be explained.
FIG. 21 is a circuit diagram of the binary digitizing unit 108
shown in FIG. 9, partially modified from that of the third
embodiment shown in FIG. 18A. The circuit shown in FIG. 21 is
different in the presence of a joint error memory 434, from that
shown in FIG. 18A.
In FIG. 21, the same components as those in FIG. 18A are
represented by the same numbers and will not be explained
further.
The joint error memory 434 is used for storing error data to be
carried over from the preceding area to the object area.
In the following there will be explained the function of the
circuit, with reference to a timing chart shown in FIG. 22 which
shows a case of a single color for each of understanding. In the
actual circuit, the number of pixels is multiplied by the number of
colors, namely four times for four colors.
A scanning operation of the CCD unit 18 in the scanner unit 1
explained before provides image data of plural lines.
In the first scanning operation for processing the object area
shown in FIG. 20, a switch SW1 is closed with the timing of a
control signal B shown in FIG. 22, whereby the error data to be
added to the image data of the 257th, 258th and 259th pixels in
each line of the post-area shown in FIG. 20 (corresponding to the
1st, 2nd and 3rd pixels in the post-area) are supplied from the
delay unit 412 and stored in the joint error memory 434. These
error data are read from the joint error memory 434, in
synchronization with the image data of the 1st, 2nd and 3rd pixels
of corresponding lines obtained in the succeeding scanning
operation. For this purpose a switch SW2 is closed with the timing
of a control signal A shown in FIG. 22. The error data thus read
are sent through the switch SW2 to the adder 427, then added to the
corresponding image data, and supplied to the error distribution
unit 431 and the comparator 432 for error distribution and binary
digitizing. Then, the error data to be added to the image data of
the 257th, 258th and 259th pixels of the post-area (corresponding
to the 1st, 2nd and 3rd pixels of an area succeeding the post-area)
are stored in the joint error memory 434 through the switch SW1 as
in the first scanning operation explained above.
Thereafter, the writing and reading of the error data of the
jointing portion to and from the joint error memory 434 are
conducted according to the timing shown in FIG. 22.
As explained in the foregoing, a smooth output image without
streaking in the jointing portion can be obtained by employing a
matrix which does not distribute the errors to the pixels in a
direction opposite to the main scanning direction, and by
conserving the error information in said jointing portion.
In this manner it is possible to completely prevent the streak
formation at the jointing portion of the image areas by storing, in
a memory, the error data generated in the image processing in such
jointing portion and conducting subsequent image processing based
on the thus stored error data.
Also as shown in the present embodiment, the use of an error
dispersion matrix which does not disperse the errors from the
object area to a preceding area avoids the necessity of error
feedback from said object area to the preceeding area already
processed. Thus, the jointing of image areas becomes very easy, and
the streak formation at the boundary of image areas can be
prevented.
Fifth embodiment
The dispersion matrix as shown in FIG. 2A has been associated with
the drawbacks explained above in the related background. The fifth
embodiment of the present invention prevents the formation of
streaking, at the boundary at areas (a) and (b) shown in FIG. 23,
by storing the data of a scanning operation (for example data of
the area (a)) in a memory converting the signal processing
direction in the main and sub scanning directions.
More specifically, the signals obtained by serial scanning as shown
in FIG. 1A are converted by a memory into the form obtained by
raster scanning as shown in FIG. 1B, then subjected to binary
digitizing with the error dispersion method, and again converted
inversely by means of a memory. Said conversion will be explained
by detail in the following.
Such a process allows the handling of partly jointed image data as
a continuous image, and the elimination of the streak formation at
the boundary of partial image areas.
In the fifth embodiment, the structures shown in FIGS. 4 to 10 and
12 are the same as those in the first embodiment and will not,
therefore, be explained.
FIG. 24 is a circuit diagram of the image processing unit 107 shown
in FIG. 9, partially modified from the circuit of the first
embodiment shown in FIG. 11.
The circuit shown in FIG. 24 is different, in the presence of a
scan conversion memory, from that shown in FIG. 11. In FIG. 24, the
same components as those in FIG. 11 are represented by the same
numbers and will not be explained further.
Referring to FIG. 24, color-sequential multi-value color
information of three colors (cyan, magenta and yellow) supplied
from the multi-value synthesis unit 106 is subjected, in the scan
conversion memory 200, to the conversion of scanning direction,
from the form of image signals shown in FIG. 1A to that shown in
FIG. 1B.
The scan conversion memory 200 is required to have a capacity at
least equal to a scanning operation of the area (a) in FIG. 1A. For
achieving a high-speed operation, there may be employed a so-called
double buffer system, in which the memory has a capacity
corresponding to two scanning operations for the areas (a) and (b),
and a half of said memory 200 is used for image data writing while
the other half is used for image data reading. Said double buffer
system will be explained in more detail later.
FIG. 25 is a circuit diagram of the binary digitizing unit 108
shown in FIG. 9, partially modified from the circuit of the first
embodiment shown in FIG. 13A.
In FIG. 25, the AND gate 327 in FIG. 13A is replaced by the scan
conversion memory 300. In FIG. 25, the same components as those in
FIG. 13A are represented by the same numbers and will not be
explained further.
The scan conversion memory 300 performs conversion of scanning
direction on the color-sequential multi-value image information of
four colors (cyan, magenta, yellow and black) supplied from the
comparator 326, from the raster-scanned image signals shown in FIG.
1B to the serial-scanned image signals shown in FIG. 1A. Namely
this is a conversion inverse to the conversion executed by the scan
conversion memory 200 shown in FIG. 24.
The scan conversion memory 300 is required to have a capacity at
least corresponding to a scanning operation of the area (a) shown
in FIG. 23, but, different from the scan conversion memory 200, the
memory capacity is reduced despite the increase in the number of
colors (black) since it handles binary images. For achieving a
high-speed operation, there may be employed, as in the scan
conversion memory 200, a called double buffer system in which the
memory has a capacity corresponding to two scanning operations for
the areas (a) and (b) and a half of the scan conversion memory 300
is used for image data writing while the other half is used for
image data reading.
In the following, the function of the circuit shown in FIG. 25 will
be explained with reference to a timing chart shown in FIG. 26,
which shows a case of a single color for each of understanding.
A signal VE1 is the main scanning section signal shown in FIG. 1B.
The above-explained function is conducted while the signal VE1 is
effective, and the result of processing is stored in the scan
conversion memory 300.
A signal VE2 corresponding to the main scanning section signal in
FIG. 1A is generated in the scan conversion memory 300 after the
conversion of the scanning direction, and the converted binary
image data are released, as the illustrated output data, in
synchronization with said section signal.
The error data in the boundary of the areas shown in FIG. 1A are
stored in the line memories 323, 324, so that no particular
consideration is required for such error data.
Now, reference is made to FIG. 27 for explaining an example of
signal conversion in the scan conversion memories 200, 300, each of
which is divided into two memory banks a, b as illustrated.
At first, in a step 1, the image data are written in the memory
bank a of the scan conversion memory 200. In succeeding steps, the
image data are stored alternately in the memory banks a and b.
On the other hand, as shown in the step 2, the signals with
converted scanning direction are read in succession from the scan
conversion memory 200, and subjected to the binary digitizing
explained above, and the binarized image data are written in
succession in the scan conversion memory 300.
Then, as shown in the step 3, the binary image signals with the
restored scanning direction are released from the scan conversion
memory 300.
In this manner the double buffer system enables high-speed scan
conversion of the image data.
Though the present fifth embodiment executes scan conversion by
means of two scan conversion memories 200, 300, it is also possible
to use the scan conversion memory 200 only and to send the
scan-converted signals directly, for example, to a laser beam
printer for image recording.
As explained in the foregoing, a conversion of scanning direction
provides a smooth output image without streaking at the boundary of
image areas, thus achieving the object of the present
invention.
Also, the present embodiment enables image scanning and image
printing in two directions, by changing the sequence of data
writing and reading in the memory.
More specifically, in FIG. 8, after the scanning in the area (1),
the scanning operation may be continued in the opposite direction
instead of returning to the correction area 68, and the obtained
signals may be inverted in the scan conversion memory. In this
manner image scanning in two directions is rendered possible.
Also, the printing operation in two directions is rendered possible
by inverting the signals in the scan conversion memory when the
carriage 34 returns in the direction B in FIG. 8.
These operations can be achieved by merely employing an up-down
counter for the address control for the signal writing and reading
of the scan conversion memory.
Such image scanning or printing in two directions enables a faster
copying operation since the time required for returning to the home
position can be dispensed with.
Also the formation of a mirror image can be easily achieved by the
switching of up-down address control for the data writing and
reading.
As explained in the foregoing, the fifth embodiment is capable of
preventing streak formation at the boundary of image areas by
conducting the error dispersion method after the image data are
stored in a memory and are subjected to a scan conversion.
Other embodiments
FIGS. 28 to 30 show other examples of image output requiring the
jointing information in the execution of the error dispersion
method.
FIG. 28 shows a case, in the above-explained copying apparatus, of
enlarging the original image and printing the enlarged image, in
four divided portions on the rolled sheet 29.
In this example, the image jointing information is required at the
broken lines between the output image areas 1, 2, 3, 4 in addition
to the image area boundaries explained before. The streak formation
at said broken lines can be prevented by the overlapped scanning
process explained in the first and third embodiments.
It is also possible to prevent said streak formation in the second
and fourth embodiments, by storing, in a memory, the error data
generated in the broken line portions among the output image areas
1, 2, 3, 4.
FIG. 29 shows a case of printing an enlarged image of an original
on four cut sheets in the copying apparatus explained in the
foregoing first to fifth embodiments or in a copying apparatus with
a printer such as a laser beam printer.
In this example, the image jointing information is newly required
at the broken-line portions intersecting the image areas 1, 2, 3,
4. In such case the streak formation can be prevented in the first
and third embodiments, by an overlapped process at all the jointing
portions of the image areas.
Also, such streak formation can be prevented in the second and
fourth embodiments, by storing, in a memory, the error data of all
the jointing portions of the image areas.
FIG. 30 shows image jointing portions in case of an image synthesis
with the copying apparatus explained in the foregoing first to
fifth embodiments.
Original image areas A, B are copied on a recording sheet with
image size changes. In this case, if the copying operation is
conducted in the order of A1, B1, A2 and B2, image jointing occurs
at the broken-lined boundary on the recording sheet.
In this case, as the copying operation is conducted in the order of
A1, B1, A2 and B2, contrary to the cases shown in FIGS. 28 and 29,
the streak formation can be prevented by the overlapped process at
the boundary between the areas A1 and A2, and at the boundary
between the areas B1 and B2.
Also, the second and fourth embodiments are applicable for the
prevention of streak formation, by storing, in a memory, the error
data at the boundary between the areas A1 and A2 and at the
boundary between the areas B1 and B2.
Thus, the present invention can resolve, in the cases shown in
FIGS. 28 to 30, the problem of image jointing in the use of the
error dispersion method.
In the foregoing embodiments the image data are binary digitized by
the error dispersion method, but the present invention is similarly
applicable to the case of digitizing into multiple levels.
The present invention has been explained by preferred embodiments
thereof, but it is not limited to such embodiments and is subject
to various modifications within the scope and spirit of the
appended claims.
* * * * *